Arsenic is a widespread toxic substance which occurs in magmatic and sedimentary minerals in association with sulfidic ores (i.e., arsenopyrite), secondary minerals (i.e., iron(hydr)oxide), and sediments enriched in organic substance. Especially in sulfidic environments, arsenic-sulfur species control arsenic solubility, mobility, and toxicity. Previous laboratory experiments have shown that thioarsenates (AsV-S species) are a major product during the dissolution of arsenic-sulfur minerals, namely orpiment, realgar, and arsenopyrite. By redox and leaching processes of arsenic-bearing sulfides, environmentally important for mine tailings and geothermal areas, thioarsenic species will be released into the groundwater and waters of thermal springs. Thus more attention has to be given to identify thioarsenic species, to asses their mobility and their environmental fate. For the determination of thioarsenic compounds, a species sensitive method is necessary. This can be done by X-ray absorption spectroscopy (XAS), with focus on the structural characterization of several species, or as in the proposed research project with ionchromatographic separation of the thioarsenic complexes and the following detection with ICP-MS (Inductively-Coupled-Plasma Mass-Spectrometry).

Because bacteria are involved in most element cycles under natural conditions, they catalyze the leaching of minerals and influence the resulting speciation and kinetics of thioarsenic products. Hence, this research project seeks to extend previous pH-depended dissolution experiments with orpiment and arsenopyrite to attempt the role of microorganisms for those reactions. The pH-depended batch experiments will be conducted with two different types of bacteria existent in arsenic-sulfuric waters, Desulfosporosinus auripigmentum and Thermus aquaticus, under aerobic and anaerobic conditions. The proposed research focuses on the investigation of the microbial influence on the speciation of thioarsenic compounds and their kinetics through the leaching of mineral arsenic-sulfides.